This invention relates to correction of chromatic aberration in optical systems containing gradient index lenses, particularly in gradient index endoscopes.
Optical images may be transferred by means of a lens system employing standard objective and relay lens sections. In applications where size is critical, e.g. in endoscopes for viewing within the body, e.g. in a joint, through a puncture wound without extensive surgical opening, a small-sized, e.g. 1 mm diameter, cylindrical rod lens system with radial index distribution (GRIN lens) may be substituted.
GRIN lenses currently available exhibit large amounts of chromatic aberration. A typical GRIN lens system exhibits a large degree of aberration in lateral color and in axial color, both typically undercorrect.
Prior efforts to correct for this aberration have been directed to the ocular system, typically a compound microscope, receiving the image from the GRIN lens system. These efforts have followed two approaches. In one approach, the microscope is designed to overcorrect for this aberration by an amount suitable to substantially correct the final image. The other approach involves adding a zero power corrector to the microscope, e.g. a cemented doublet of two glasses with the same principal index but widely differing dispersions and plano outer surfaces. Both approaches have had limited success in practical systems due to the precise alignment required between the ocular and GRIN lens systems in order for the correction to have the calculated corrective effect.